Formation of a weakly diverging caustic beam in an underwater sound channel open to the bottom

The paper studies the patterns manifesting themselves in the formation and propagation of caustic and weakly diverging beams using the geometric acoustic approximation and mode theory applied to the simplest model of an underwater sound channel open to the bottom in the form of the bilinear dependence of the square of the refractive index on depth. It is established that when a vertical array emitting a tonal sound signal is located at a certain critical depth, the multimode caustic beam which forms near the reference ray horizontally departing from its center and which predominates in intensity is simultaneously the most weakly diverging beam. It is shown that the reference ray of such a weakly diverging caustic beam corresponds to the smoothest minimum for the dependence of the length of the ray cycle on their angle of departure from the center of the array and to the depth level of revolution at the critical depth characteristic of the given oceanic waveguide.     

Luminescence of Single Semiconductor Nanocrystals at Room Temperature as Observed with Confocal Microscopy

Optics and Spectroscopy - Luminescent images of a few distinguishable alloyed semiconductor quantum dots obtained at room temperature using confocal scanning microscopy with spectral and temporal...     

Characteristics of the reverberation signal at a vertical array with tonal insonification of a shallow-water basin

The angular and spectral characteristics of reverberation signals on a fixed path are studied by using vertical receiving arrays with a tonal insonification of the basin. The choice of the frequency range F ～ 200–300 Hz is caused, first, by the low propagation loss and the availability of high-power acoustic transducers for this range and, second, by the possibility to study the phenomena of sound scattering by the sea surface for comparable wavelengths of surface and acoustic waves. The data of experiments on two paths are considered: the first path is in the Barents Sea with propagation conditions corresponding to a uniform waveguide with sea depths H ～ 110–120 m, whereas the second path is in the White Sea with propagation conditions corresponding to a nonuniform waveguide where the sea depth varies from 30 to 250 m.     

Caustics and weakly divergent beams in oceanic waveguides

It is found that the weakly divergent beam formed around the reference ray with minimal cycle length does not stand out in intensity against the background of the total field. It is shown that, under the same conditions, another beam stands out in intensity: it is the caustic beam composed of the system of caustic lines, which are the envelopes of the family of rays forming the weakly divergent beam.     

Synthesis and molecular structure of the complex YbI(bipy)(DME)2

The reaction of the naphthalene complex of ytterbium, [Yb(DME)₂]₂(μ-C₁₀H₈), with 2,2′-bipyridine in 1,2-dimethoxyethane afforded the Yb^II complex containing the 2,2′-bipyridine radical anion. The resulting complex YbI(bipy)(DME)₂ was characterized by IR and ESR spectroscopy, X-ray diffraction analysis, and magnetochemistry. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2341–2344, November, 1998.     

Predicting biotransformation potential from molecular structure

The program PASS-BioTransfo is presented, which is capable of predicting many classes of biotransformation for chemical compounds. A particular class of biotransformation is defined by the chemical transformation type and may additionally include the name of the enzyme involved in a transformation. An evaluation of the approach is presented, using biotransformations taken from the databases Metabolite (MDL) and Metabolism (Accelrys), respectively. When trained with biotransformations from Metabolite, PASS-BioTransfo predicts 1927 classes of biotransformation; the average accuracy estimated in LOO cross-validation is about 88%. After training with the biotransformations from the Metabolism database, 178 classes of biotransformation are predicted with an average accuracy of about 85%. The results of cross-prediction with several training and evaluation sets are presented and discussed.     

Robustness of biological activity spectra predicting by computer program PASS for noncongeneric sets of chemical compounds

The computer system PASS provides simultaneous prediction of several hundreds of biological activity types for any drug-like compound. The prediction is based on the analysis of structure-activity relationships of the training set including more than 30000 known biologically active compounds. In this paper we investigate the influence on the accuracy of predicting the types of activity with PASS by (a) reduction of the number of structures in the training set and (b) reduction of the number of known activities in the training set. The compounds from the MDDR database are used to create heterogeneous training and evaluation sets. We demonstrate that predictions are robust despite the exclusion of up to 60% of information.     

STRUCTURE AND CATALYTIC PROPERTIES OF (ACETYLACETONATO-κ2O,O′)BIS(TRI(2-FURYL)PHOSPHINE) PALLADIUM(II) TETRAFLUOROBORATE

Journal of Structural Chemistry - Reaction of Pd(acac)2 with BF3·OEt2 in the presence of tri(2-furyl)phosphine in toluene yields complex [Pd(acac)(TFP)2]BF4 (I) (TFP is tri(2-furyl)phosphine)...     

Formylation of 4,7‐Dihydro‐1,2,4‐triazolo[1,5‐a]pyrimidines Using Vilsmeier–Haack Conditions

Formylation of 5‐methyl‐7‐phenyl‐4,7‐dihydro‐1,2,4‐triazolo[1,5‐a]pyrimidine 1a using Vilsmeier–Haack conditions yields 5‐methyl‐7‐phenyl‐4,7‐dihydro‐1,2,4‐triazolo[1,5‐a]pyrimidin‐6‐ylcarbaldehyde 3a . 5,7‐Diaryl‐4,7‐dihydro‐1,2,4‐triazolo[1,5‐a]pyrimidines 1b , 1c in this reaction apart from formylation undergo recyclization into 5‐aryl‐1,2,4‐triazolo[1,5‐a]pyrimidin‐6‐ylmethane derivatives 4b , 4c , 5b , 5c , and 6 . The structure of the synthesized compounds was determined on the basis of NMR, IR, and MS spectroscopic data and confirmed by the X‐ray analysis of the 6‐(ethoxy‐phenyl‐methyl)‐5‐phenyl‐[1,2,4]triazolo[1,5‐a]pyrimidine 6 , 5‐phenyl‐6‐(1‐phenyl‐vinyl)‐[1,2,4]triazolo[1,5‐a]pyrimidine 11 , and 7‐phenyl‐6‐(1‐phenyl‐vinyl)‐[1,2,4]triazolo[4,3‐a]pyrimidine 12 .     

Algorithms for converting 3D surface roughness spectra when calculating frequency-angle reverberation characteristics

On the basis of an earlier developed model of sound scattering by surface disturbances characterized by 3D roughness spectra, we propose and test a sufficiently fast algorithm for calculating the spectral power density of surface reverberation that takes into account the propagation conditions, distance, and beam pattern of the receiver system. For a distance of up to 1000 m, a water area depth of ??20 m, and actually measured 3D roughness spectra in the Doppler frequency range of ±5 Hz, we have calculated the frequency-angle reverberation spectra for an acoustic background-radiation signal of 1.5 kHz. The obtained angle and frequency reverberation characteristics are compared with the results of acoustic measurements conducted using linear horizontal receiver antennas.